In some types of wider implements, it is known to fold the wings of the implement from a field position, where right and left wings are extended substantially perpendicular to the operating travel direction, rearward and backward to a transport position where the wings are substantially parallel and aligned in the travel direction. Such an implement is disclosed for example in U.S. Pat. No. 4,821,809 to Summach et al. which discloses a rear folding drawbar such as would be used for carrying harrows, packers, and the like. Rear fold transport is relatively inexpensive compared to transport systems where the wings are folded upward.
Rear fold is therefore popular with relatively lighter implements such as harrows, sprayers, packers, and the like which are relatively easy to pull, and typically are very wide. Rear fold is also popular for land rollers which typically comprise large and heavy cylindrical drums mounted to the center section and to each wing for rolling land to smooth the surface and push rocks and the like into the ground to facilitate harvesting short crops.
A typical implement will have a center section mounted on fixed wheels, with the right and left wings pivotally attached to corresponding right and left ends of the center section about a vertical axis. Wheels supporting the outside ends of the wings are typically castering wheels free to pivot about a vertical caster axis so as to roll along the ground in any direction as dictated by the position of the wing. In the field position the wings are typically maintained perpendicular to the operating travel direction by a cable, bar, or like brace extending forward and inward from a middle portion of the wing to the center section.
When moving from the field position to the transport position, the braces are released and as the towing vehicle moves the center section forward, the wings fall back into alignment with the operating travel direction and the wheels caster into alignment with the operating travel direction. With implements where the wings are light, such as agricultural sprayers, often the operator or manually moves the wings out from the transport position to the field position and attaches the braces. However where the wings are heavier, such as with harrows, packers, land rollers, and the like, moving from the transport position to the field position requires maneuvering the wings by turning to one side, backing up, or the like such that one of the wings extends laterally from the center section so that the brace can be attached, and then turning the opposite way or backing up to similarly orient the other wing and attach the brace for it.
It is also known to provide a mechanism for pulling the wings forward, such as that disclosed in U.S. Pat. No. 4,709,857 to Wilger directed to transport system for a sprayer. In the Wilger sprayer the wing wheels are controlled by a hydraulic cylinder that moves them 90 degrees with respect to the wing. In the transport position the wheels are aligned parallel with the wing. To move from transport to field position the implement is stopped in the field, and the wing wheels are moved 90 degrees such that the wheels are perpendicular to the wing. A power fold arm then pulls the wings outward and forward to the field position where the wheels are aligned with the operating travel direction in the field position, and braces are latched to maintain the wings in the field position. The implement may then be moved forward.
Rear folding agricultural sprayers with their light weight wings present relatively minor challenges compared to the much heavier implements used for seeding and ground working where the wings are relatively massive and heavy. U.S. Pat. No. 6,374,921 to Friggstad discloses an air seeder where the wings fold forward instead of rearward.
It is becoming more common to pull a chain of implements and carts behind one tow vehicle. For example in an air seeder there may be a cart carrying agricultural products at the front, then the air seeding implement hooked to the cart, then a fertilizer wagon hooked to the air seeder, then perhaps a packer hooked behind the fertilizer wagon. It is not practically possible to maneuver a conventional rear fold implement from the transport to field position as described above because it is almost impossible to back up a chain of two or three implements. The system of Wilger, when adapted to a heavy implement such as an air seeder or a land roller, requires a costly and cumbersome mechanism that is able to exert very high forces on the wings in order to draw them forward from transport to field position.